"Sentinel" by Mark Greaney is a thrilling novel published by Penguin Publishing Group in 2024. The book is part of the Armored Ser. series and offers a gripping storyline filled with espionage, political intrigue, and action & adventure. With a hardcover format and 496 pages, this fiction novel is sure to captivate readers with its intense plot and engaging storytelling by the talented author Mark Greaney.